Electrical heaters



Original Filed March 11, 1960 Oct. 11, 1966 H. F. DICKSON, JR., ET AL3,277,685

ELECTRICAL HEATERS 5 Sheets-Sheet l U 56 /ZZ :51 g. E l 36 I 4/ 3.9 39INVENTORS 4 HERBERT E D/c/rso/v Jv.

PAUL rv /ms ATTORNEY Oct. 11, 1966 DICKSON, JR" ETAL 3,277,685

ELECTRICAL HEATERS Original Filed March 11, 1960 3 Sheets-Sheet 2 fly;-7

IN VENTORS HERBERT i. D/cnso/v JR.

7nuL Hans ATTORNEY Oct. 11, 1965 o c so JR" ETAL 3,277,685

ELECTRICAL HEATERS Original Filed March 11, 1960 5 Sheets-Sheet 5 PAULHxms ATTORNEY United States Patent 3,277,685 ELECTRICAL HEATERS HerbertF. Dickson, Jr., and Paul Haas, Seneca Falls,

N.Y., assignors to Sylvania Electric Products Inc., a corporation ofDelaware Original application Mar. 11, 1960, Ser. No. 14,471, now PatentNo. 3,160,946, dated Dec. 15, 1964. Divided and this application June12, 1963, Ser. No. 287,401 Claims. (Cl. 72-146) This application is adivision of Serial No. 14,471, filed March 11, 1960, entitled ElectricalHeaters, now Patent No. 3,160,946, issued on December 15, 1964, andassigned to the same assignee as the present invention.

This invention relates to heaters for electrical devices and moreparticularly to heaters adapted for use with thermionic cathodes of thetype employed in electron tubes.

It has been proposed that a low heater power type of cathode assemblymay be used in electron tubes. One form of such a heater-cathodeassembly employs an insulated heater wire embedded in the cathode base.In this structure the cathode base metal material in powdered form isdeposited about the heater wire and subsequently the powder is pressedinto a pellet and sintered.

It is difiicult to make a satisfactory heater embedded cathode assembly.The pellet itself is small and the requirements for electron emission atlow heater power are such that a considerable length of the heater wiremust be packed within the pellet. In order to achieve the proper uniformtemperature of the cathode pellet, the heater should physically beuniformly and symmetrically placed, there should be no shorted sectionsof the heater, and the heater-cathode leakage should be a minimum.

The fabrication of the heater itself is an important factor in achievingthe requirements enumerated above. For instance, the heater wire shouldbe formed into a configuration to provide a relatively large amount ofwire Within the pellet, and the configuration should be symmetrical withuniform sectional spacings. In addition, the insulating coating shouldbe of uniform thickness over the enitre embedded heater portion.

Accordingly, it is an object of this invention to fabricate a heateradapted for use in heater embedded cathode assemblies.

It is a further object to form a substantially fiat heater coil withuniform coil wraps, uniform spiral turn spacings, and a uniform coating.

The foregoing objects are achieved in one aspect of the invention by theprovision of a process and apparatus for forming a spiral reverse coilwound heater. The resistance heater wire is spiral wound upon a mandreland this wire spiral and mandrel assembly are subsequently twisted intoa reverse wound flat coil with substantially uniformly spaced wraps. Themandrel is then removed and the heater wire spiral is coated withinsulating material. In the coil winding operation, the mandrel isplaced in a chuck and twisted with the ends of the mandrel arrested fromrotational movement by stop pins.

For a better understanding of the invention, reference is made to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 illustrates a length of heater wire spiral wound upon a mandrel;

FIG. 2 shows the heater coil winding device;

FIG. 3 is an enlarged top view of the heater winding chuck employed withthe device of FIG. 2;

FIG. 4 illustrates a cross-sectional view of the heater winding device;

FIGS. 5, 6, and 7 illustrate the manner reverse heater coil;

of forming the 3,277,685 Patented Oct. 11, 1966 method of annealing theformed FIG. 8 illustrates the heater coil;

FIG. 9 shows the manner of removing the mandrel from the heater spiral;

FIG. 10 illustrates the heater coating operation; and

FIG. 11 is a plan view of a finished spiral reverse coil wound flatheater.

Referring to the drawings, a spiral reverse wound substantially fiatcoiled heater 13 is shown in FIG. 11. The heater resistance wire 15 isformed into a spiral which is in turn twisted as a reverse wound coil.Each turn of the spiral is coated with an electrical insulating material17 except the last several turns. The straight wire ends 19 are leftuncoated to allow for welding to the heater power supply leads whenemployed in an electron tube.

Heater 13 is uniquely adapted to provide maximum heat for a given areawith minimum power. Due to its relatively small size, compactness anduniform spacing and symmetry, the heater is suitable for use in anindirectly heated cathode assembly wherein the heater is embedded in thecathode base material. This type of cathode assembly is shown anddescribed in co-pending application S.N. 14,472, now Patent No.3,097,419, issued on July 16, l963,'entitled Heater-Cathode Assemblies,filed concurrently herewith by the common assignee.

FIG. 1 illustrates a spiral length of heater wire 15 which has beenselected to provide the heat necessary for a given application at agiven power rating. The wire, which may be tungsten, is wound upon amandrel 21 made of, for instance, molybdenum. The diameter of thewire,turns per inch of the spiral, and length of the heater can be varied inorder to produce the desired electrical characteristics. In the spiralwinding operation, the wire 15 is preferably stretched beyond theelastic limit so that the initial spiral shape will be substantiallymaintained after mandrel 21 has been removed as will be hereafterdescribed.

The mandrel and wire spiral assembly 22 are subsequently formed ortwisted into a substantially fiat reverse wound coil. A winding device23 is provided for the purpose of accomplishing this reverse windingoperation. Referring to FIGS. 2-7, device 23 comprises a cylindricalblock 25 having an aperture 27 extending longitudinally therethrough.The upper heater supporting surface 29 may be tapered a slight amount,e.g., several degrees, radially symmetrically downward from aperture 27toward the periphery of the block 25 to prevent the wire spiral fromclimbing over itself during the twisting operation.

Mounted upon surface 29 are two frusto-conical shaped arresting pins 31.The small diameters of the pins lie adjacent surface 29 so that the pinsare beveled outwardly to prevent the ends of mandrel 21 from ridingupwardly and to provide a drag on the mandrel during the coil wrappingoperation. Pins 31 preferably exceed the height of the spiral of wireand are oppositely disposed from and equally radially spaced from thecenter of aperture 27. For simple reverse wound coils, the pins may bepermanently located as shown. However, for larger or more intricate coilconfigurations, it may -be desirable to either move the pins radiallyduring the winding operation or to raise and lower a plurality of pinssequentially from surface 29.

Block 25 rests upon a cylindrical base 33 having a rod 35 passingthrough aperture 27. The upper end of the rod has a chuck 36 formed witha spiral and mandrel assembly receiving slot 37 defined by laterallyspaced slot walls 39. The opposed outside edges 41 of the walls arerecessed from the rod periphery and are curved to meet a portion of therod periphery to provide the initial coil wrap configuration. The heightof the walls preferably exceed the diameter of the wire spiral. Sinceblock 25 merely rests upon base 33, these parts may be rotated relativeto one another. The amount of rotation of, for instance, base 33 orchuck 36 relative to block 25 may be ascertained from pointer 43 andmarkings 45. Also, base 33 and block 25 may reciprocate longitudinallyrelative to one another so that chuck 36 can be retracted to a mandrelassembly release position.

In the reverse coil winding operation, assembly 22 is first placedwithin slot 37 as shown in FIG. 2. When a symmetrical reverse coil suchas is illustrated in FIGS. 7 and 11 is desired, the center of assembly22 is positioned at the center of the slot. The initial partial Wrap ofthe coil is achieved by applying tension to the mandrel and rotatingbase 33 to provide rotation of chuck 36, FIG. 5. The tension may beapplied by holding the ends of mandrel 21 to provide drag and thereforebending around the edges 41 of walls 39, or it may be accomplished bypressing downwardly against the spiral and mandrel to achieve the sameresults. After the partial first wrap is made, chuck 36 is furtherrotated until assembly 22 contacts arresting pins 31. Continued rotationof the chuck wraps the spiral wire and mandrel assembly as shown in FIG.6. Due to the beveled sides of arresting pins 31, assembly 22 tends tobecome trapped between the pins and the upper block surface 29. Thistrapping action creates a drag on the mandrel and thereby providesrelatively tight Wrapping. During this latter rotational movement, someoverwrappin-g is desired. The amount of overwrapping depends upon thespacing re quired between sections of the coil 13.

After the spiral wire and mandrel assembly 22 have been wound as areverse coil as shown in FIG. 6, chuck 36 is then rotated in theopposite direction. During this rotation, assembly 22 contacts pins 31on the opposite sides thereof, which causes the coil to unwrap an amountsufiicient to provide the coil spacing desired, see FIG. 7. The ends ofthe coil thereby extend tangentially from the curvature of the outsideturns. Rod 35 with its chuck 36 is then retracted into aperture 27 torelease the substantially flat reverse coil formed from assembly 22. Thereleasing operation is achieved by moving base 33 or block 25longitudinally away from one another.

After assembly 22 has been wound into a reverse coil, it is placed in anoven (not shown) and fired between flat tungsten plates 47, see FIG. 8.The firing operation may be performed in a wet hydrogen reducingatmosphere in accordance with the temperature-time relationship requiredfor annealing wire 15 and mandrel 21. The substantially fiat coil isthen immersed in a solution 49 which removes the mandrel by selectiveetching, see FIG. 9. A suitable solution such as one consisting of 50percent nitric acid, 30 percent sulfuric acid, and 20 percent water byWeight is capable of etching a .002 inch diameter molybdenum mandrel ina relatively short time without attacking the tungsten wire 15.

The reverse wound coil of wire may be subsequently rinsed in deionizedwater and subsequently electrophoretically coated in tank 50 with theinsulating material 17. During the coating operation, the coil of wire15 is held in electrode 51, FIG. so that the area to be coated isexposed to coating bath 53, which may consist of a dispersion ofaluminum oxide in a partially hydrolized aluminum nitrate and alcoholsolution. Electrode 51 shields the last several turns of wire and theends 19 so that no coating is deposited thereon. The uncoated portionsof the wire are utilized for a welding connection during ultimateassembly in an electron tube. An anode 55 is also disposed in bath 53,and positive and negative potentials are applied to anode 55 andelectrode 51 respectively to electrophoretically coat wire 15 in amanner well understood in the art. Due to the uniformity of spacingbetween the spiral turns and coil wraps, the insulating coating isuniformrly deposited over the desired area.

After coating, wire 15 is subsequently fired between flat plates of thetype shown in FIG. 8. Here again, a wet hydrogen atmosphere may be usedduring this operation. Firing of the wire assures flatness of the coil,it removes any distortion in the reverse coil wraps, and it sinters theinsulating coating 17 to produce the reverse coil wound spiral heater13, shown in FIG. 11.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention as defined by the appendedclaims.

What is claimed is:

1. A device for winding turns of heater wire comprising a block having aheater supporting upper surface and an aperture extending longitudinallytherethrough, a lurality of heater movement arresting pins mounted uponsaid surface and radially spaced from said aperture, and a rod rotatablymounted in said aperture having a heater chuck formed at the end thereofto twist the heater wire during rod rotation into a substantially flatreverse wound coil having uniform spacing and symmetry While the ends ofsaid Wire are arrested from rotational movement.

2. A device for winding turns of heater wire comprising a block having aheater supporting upper surface and an aperture extending longitudinallytherethrough, and a plurality of outwardly beveled heater arresting pinsmounted upon said upper surface, the pins being radially spaced equallyfrom said aperture, in combination with a rod rotatably mounted in saidaperture formed to provide a chuck at the end thereof having a heaterwire receiving slot therein to provide upon the rotation of said rod asubstantially flat reverse wound coil having uniform spacing andsymmetry.

3. A device for winding turns of heater Wire comprising a block having aheater supporting upper surface and an aperture extending longitudinallytherethrough, said upper surface being tapered radially symmetricallydownward from the aperture toward the periphery of said block, and twooutwardly beveled heater arresting pins mounted upon said upper surface,the pins being oppositely disposed from and radially spawd equally fromsaid aperture; in combination with a rod rotatably mounted in saidaperture formed to provide a chuck at the end thereof with a heaterreceiving slot formed by laterally spaced Walls.

4. A device for Winding turns of heater wire comprising a block having aheater supporting upper surface and an aperture extending longitudinallytherethrough, said upper surface being tapered radially symmetricallydownward from the aperture toward the periphery of said block, and twofrustro-conical shaped heater arresting pins mounted with the smallerdiameters thereof upon said upper surface, the pins being oppositelydisposed from and radially spaced equally from said aperture; incombination with a rod rotatably mounted in said aperture formed toprovide a chuck at the end thereof with a heater receiving slot formedby laterally spaced walls, the opposed outside edges of said walls eachbeing recessed from the rod periphery and having a curvature to meet aportion of the rod periphery to provide a substantially symmetricalinitial coil wrap configuration.

5. A device for winding turns of heater wire comprising a block having aheater supporting upper surface and an aperture extending longitudinallytherethrough, said upper surface being tapered radially symmetricallydownward from the aperture toward the periphery of said block, and twofrustro-conical shaped heater arresting pins mounted with the smallerdiameters thereof upon said upper surface, the pins being oppositelydisposed from and radially spaced equally from said aperture; incombination with a rod rotatably mounted in said aperture formed toprovide a chuck at the end thereof with 5 6 a heater receiving slotformed by laterally spaced walls, References Cited by the Examiner theopposed outside edges of said Walls each being UNITED STATES PATENTSrecessed from the rod periphery and havmg a curvature formed to meet aportion of the rod periphery to provide 1,841,784 1/1932 Brown 72-456 asubstantially symmetrical initial coil Wrap configura- 5 FOREIGN PATENTStion, said chuck being reciprocatingly mounted in the 1178 741 12/1958France block aperture for movement between an extended heater Windingposition disposed above said upper surface and CHARLES LANHAM Primm'yExamine" a retracted heater release position. R. D. GREFE, AssistantExaminer.

1. A DEVICE FOR WINDING TURNS A HEATER WIRE COMPRISING A BLOCK HAVING AHEATER SUPPORTING UPPER SURFACE AND AN APERTURE EXTENDING LONGITUDINALLYTHERETRHOUGH, A PLURALITY OF HEATER MOVEMENT ARRESTING PINS MOUNTED UPONSAID SURFACE AND RADIALLY SPACED FROM SAID APERTURE, AND A ROD ROTATABLYMOUNTED IN SAID APERTURE HAVING A HEATER CHUCK FORMED AT THE END THEREOFTO TWIST THE HEATER WIRE DURING ROD ROTATION INTO A SUBSTANTIALLY FLATREVERSE WOUND COIL HAVING UNIFORM SPACING AND SYMMETRY WHILE THE ENDS OFSAID WIRE ARE ARRESTED FROM ROTATIONAL MOVEMENT.